Other than the usability differences, the underlying technology is significantly different. ZumoDrive uses its own file system layer instead of WebDAV(what most drive services use). What this means for the user is that the drive is a lot faster to access, and it supports things like streaming & random access of files.

I think that JungleDisk would be much harder for an average user to install. I haven't used it, but I did just install Zumodrive. I think that linking up with an s3 account is something that an average end user would rather not have to worry about.

I'm a Jungle Drive user, and while I don't pretend to be an "average" user, it was very easy to install. I'm not sure if setting up an Amazon S3 account and then putting the key into Jungle Drive would be too technical for the average user, maybe it would. Overall I've been very happy with Jungle Drive so far, and the $20 one time charge is pretty nice, particularly since I can use that on as many machines as I want with one Amazon account.

How does that compare with ZumoDrive?

--Disclosure - not currently a user of ZumoDrive

also what the difference between zumodrive and dropbox (other yc co.)????

At least one thing: Dropbox synchronizes its directory, meaning that every machine linked to your account has a local copy of the data stored there. Zumodrive keeps most things remote, unless you explicitly ask to have a local copy (seems to support some form of policies for which things should be local). In theory, then, Zumodrive lets you go beyond your disk capacity, but it's a bit too expensive to just offload hundreds of gigabytes.

Also, Zumodrive doesn't seem to have sharing like Dropbox does..?

Zumodrive actually supports sharing either by a public link or to a private email address. There is a share option in the right click context menu as well as on the web file browser.